Exam questions Flashcards
Which gems form by metamorphism?
The metamorphic rocks of East Africa produce tanzanite as well as ruby, emerald, alexandrite, and tsavorite, among others
Which gems can crystallize in volcanic rock from gases released by magma
Both red beryl and topaz can crystallize from gases released by magma during the final cooling stages
Which is a key locality for hydrothermal gems?
Ouro Preto, Brazil. Imperial topaz from Brazil and emeralds from Colombia are important hydrothermal gems
From granite, pegmatite gems get exotic elements like
Beryllium, boron, and lithium are the elements commonly found in pegmatites
Heat and pressure transform limestone into
The limestone deposits of Mogok, Myanmar, are converted to marble by heat and pressure.
Kunzite is most often found in association with
Tourmaline, beryl, and kunzite are all found in association with pegmatites.
Myanmar’s famous Mogok ruby deposits were formed by
metamorphic processes.
Synthetic gem materials
are not minerals because they’re grown in a laboratory rather than in the earth
Which gems are cryptocrystalline aggregates?
Chalcedony and turquoise
Crystals that grow in a flux that is highly saturated with the necessary elements tend to be
SMALL. If the flux is very highly saturated with the elements necessary for crystal growth, many small crystals tend to grow
What Gem materials are commonly twinned?
quartz, feldspar, corundum, and spinel
Which element causes the color of both almandine and peridot?
Iron is the element that causes the red in almandine and the yellowish green in peridot
Which components of a transition element’s atoms can produce color in gems?
Electrons are the components of a transition element’s atoms that produce color in gems.
What is the only type of gem that can show pleochroism?
Only doubly refractive gems can show pleochroism.
Which gems can show three pleochroic colors?
tanzanite and andalusite, iolite
Which element does chromium substitute for to cause ruby’s red?
Aluminum
In many blue sapphires, the intervalence charge transfer that causes the color is between
iron and titanium
The hydrothermal growth process is the only method used to produce which synthetic gem?
Quartz
A snakeskin or honeycomb structural pattern is typical of
synthetic opal.
Synthetic turquoise and lapis lazuli is most likely produced by which process?
Ceramic
Which gems are not heat treated
Iolite, rhodolite, and tsavorite
After irradiation, which gem’s color is stable under normal wearing conditions?
Golden beryl
How deep is the color layer that lattice diffusion with titanium or chromium creates in corundum?
0.01 to 0.50 mm
What agent can create a shallow layer of asterism when it’s introduced below the surface of a corundum cabochon by lattice diffusion?
Titanium oxide. Lattice diffusion creates a shallow layer of asterism in corundum by introducing titanium oxide below the surface. After slow cooling over several days, the titanium oxide crystallizes into rutile needles, which cause the asterism
Heat treatment in a reducing environment can
in sapphire
deepen blue color in sapphire
The vast majority of Sri Lankan deposits are in
alluvial gravels
The finest ruby has a pure, vibrant red to
slightly purplish red hue with medium to medium-dark tone and vivid saturation
The earth’s three most abundant elements are oxygen, silicon, and aluminum.
All corundum varieties are made of aluminum oxide, a mixture of aluminum and oxygen.
Corundum can form only
in an environment with low silicon content
The most renowned rubies, like those from Myanmar, Afghanistan, and northern Vietnam, typically forms in marble during __________ formation process?
metamorphic process, when heat and pressure act on existing limestone deposits. The rubies are found in irregularly distributed layers within the surrounding marble
Iron content inhibits fluorescence, so even if a basalt-hosted ruby’s
hue is excellent, it won’t have the fluorescence of a marble-hosted ruby (Marble iron content is low).
Iron-rich rubies often appear _____.
dark
In rubys: Strong iron content reduces fluorescence, while _______
iron content causes highly visible red fluorescence that brightens ruby
color.
low
Typical _____ clarity characteristics include silk (rutile needles), boehmite needles, included crystals, fingerprint inclusions, growth zoning, and color zoning.
ruby
Heating thai/Cambodian rubies at relatively moderate temperatures of 800° to
1250°C (1472-2282°F) in an _______ environment removed the blue
color and produced a more marketable, pure red hue
oxidizing
_________-temperature heat treatment can sometimes improve ruby color by
removing blue or brown secondary colors, but it is difficult to detect.
_________-temperature heat treatment can improve ruby clarity as well as color.
low, high
__________ lattice diffusion is difficult to detect and often requires laboratory
analysis.
Beryllium
_______ has replaced _________ as the source of the majority of the world’s ruby.
Africa, Southeast Asia
The _________ area of Mozambique has emerged as the world’s most important
ruby source.
Montepuez
The most highly valued blue sapphires are _______blue to _______ blue, in
medium to medium-dark tones, with strong to vivid saturation.
velvety blue to violetish blue
The trace elements _____ and _________ cause the blue of sapphire.
iron and titanium
Blue sapphires can originate in basaltic or non-basaltic environments.
Sapphires that originate in ________ are generally richer in iron than sapphires
from _________ sources.
basalt, non-basaltic
Non-basaltic sapphires form under a variety of conditions, primarily
__________. Sources include Myanmar, Kashmir, Sri Lanka, and most Madagascar deposits
metamorphic
Pleochroism in blue sapphire typically appears as a variation between
slightly_________ blue and slightly_________ blue in different crystal
directions.
greenish, violetish
When a sapphire cutter orients the table facet___________ to the optic axis direction, the finished stone’s face-up color displays more of the
preferred violetish blue and less of the greenish blue hue.
perpendicular
Geuda is heated to around 1250°C (2282°F) in a ___________ environment. If the right concentrations of _________ and ________ are present, a uniform fine blue color results, along with considerable improvement in transparency and luster.
reducing, iron and titanium
Heat-treated geuda and_________ make up a significant portion of the commercial quality
blue sapphire market.
dhun
Most fine sapphires over _____ carats are from _________________
100, Sri Lanka
Which gemstone occurs in almost every color?
Tourmaline
What two coloring agents are usually responsible for color change in gemstones?
Chromium and vanadium
Translucent to opaque rough is usually cut as a ____________ as opposed to being faceted
cabochon
Which colored stone variety has cutting challenges due to vulnerable cleavage planes?
Tanzanite has two directions of cleavage
Gems that are usually eye-clean include
spodumene, yellow beryl, and aquamarine
If an emerald weighs 3.50 cts., with a cost of $10,500.00, what is its per-carat price?
$3,000.00
What is the cost of a ruby that weighs 5.76 cts. and has a per-carat price of $5,500.00?
$31,680.00
When you first start to count a large pile of small gems, it’s best to separate them into groups of
5
Differing amounts and combinations of the trace elements iron, titanium, and____________ cause most fancy sapphire colors.
chromium
The trace element_____________ causes sapphire’s color change.
vanadium
The typical corundum color change is from blue/violet in daylight to___________ purple to strongly_____________ purple in incandescent light
violetish, reddish
Stars are usually made up of 2, 3, or____ intersecting bands, resulting in 4, 6, or__ rays. The most common being 6 rays
6, 12
Hematite inclusions cause the asterism in_______ star sapphires.
black. The sapphire’s bodycolor is actually yellow, green, or blue, but the inclusions make it appear dark brown or black.
The sapphire’s________ is actually yellow, green, or blue, but the inclusions make it appear dark brown or black.
bodycolor
_____________ produces what some consider the widest range of fancy sapphire colors
in the world
Sri Lanka
_______________ is a major source of high quality pink sapphire/ruby
Madagascar
_______________ of sapphire can produce padparadscha colors as well as highly saturated yellows and oranges
Beryllium diffusion
Ruby deposits in Thailand and Cambodia are associated with
alkali basalt
The rubies found in the mountains of Tajikistan, Afghanistan, and Pakistan are all ________ hosted
marble
The flame-fusion method for creating synthetic rubies is also known as
the Verneuil method
The most common crystal habit for ruby is the
tabular hexagonal prism, but crystals from some sources can be elongated prisms and bipyramids
Which of the following have inclusions and growth structures that might closely resemble natural rubies?
Flux and hydrothermal synthetics
Blue sapphire’s most common crystal habit is a(n)
spindle-shaped hexagonal pyramid or bipyramid
Regions associated with basalt-related sapphire include Cambodia, Thailand, _________ and ___________
Nigeria, and Australia
Fancy sapphires from Montana tend to be
light in tone
______star sapphires, however, are prone to parting, so they’re usually cut very flat to reduce the risk of damage
Black
Color-change sapphire typically changes from blue or violet to
strongly reddish purple
The best and most expensive star corundum is________-transparent, with just enough silk to create a well-defined star. Too much silk can harm__________ and also lead to poor color, lowering the value of the stone considerably
semi, transparency
